The present invention relates to a non-destructive inspection probe for an internal wall of a duct, more particularly an internal wall of a duct in a nuclear power plant.
The invention likewise relates to a set of probes comprising multiple inspection probes.
In many industrial installations it is necessary to periodically carry out a check on the internal walls of ducts to verify that they are intact and in the interests of their operational reliability and safety. Operators are therefore obliged to perform increasing numbers of checks, for example on areas linking together the various elements and, should the need arise, to perform repairs of any faults that may have been detected.
This is, for example, the case with the internal walls in respect of passages in vessel floors in nuclear power plants of the pressurised water type.
The reason for this is that these passages in the vessel floor feature one end, projecting beneath the convex floor, joined to a non-rigid measurement duct allowing the floor of the vessel to communicate with a control room located within the fabric of the reactor building. Each of the ducts and the corresponding passage in the vessel floor can be negotiated with the finger of a glove in which a measurement probe is moved.
In order to enhance the operational reliability of nuclear reactors it is necessary to check the condition of the vessel floor cross-pieces to make sure that these pieces are still intact after the reactor has been operating for some time, particularly in the area where these cross-pieces are welded to the floor of the vessel.
This is also the case with the tubes of the steam generators with which nuclear reactors are fitted, which need to be examined on a regular basis.
To carry out these checks it is known to use probes, notably Foucault current probes and ultrasonic probes, which are moved along the internal wall of the duct under test.
The probes that have hitherto been used, and in particular ultrasonic probes, comprise at least one sensor mounted in a substantially cylindrical metal jacket made, for example, of aluminium or stainless steel, which has means for pressing said probe flat against the internal wall of the duct. These pressing means are constituted by a metallic spring that is generally positioned beneath the sensor or by a brush arrangement with soft bristles, usually disposed radially in order, first and foremost, to centre the probe in the duct.
Another type of probe is currently used to check an internal wall of an annular space such as a cover cross-piece for a nuclear reactor vessel fitted with a heat sleeve constituted by a coaxial internal duct.
However, these types of probes do not allow uniform contact between the sensor and the internal wall to be obtained while the sensor is being displaced within the duct, on account of the distortions and irregularities in the surface of said internal wall after the installation has been operating for some years.
In fact, the effectiveness of the test depends upon the effectiveness of the contact between the sensor and the internal wall of the area of duct under test, so much so that these contact defects manifest themselves as distortions in the test signals supplied by the probe.
It is the object of the present invention to propose an inspection probe that avoids these drawbacks by providing reliable, uniform contact between the sensor and the internal wall and that makes it possible to prolong the probe's useful life, while at the same time reducing manufacturing costs.